Magnetic devices, such as inductors and transformers, serve a wide variety of essential functions in many electronic devices. In power supplies, for example, inductors are used as choke coils for energy storage and to minimize noise and AC ripple, and transformers are used to change voltage level and to provide isolation. Such devices are often made of a magnetic core, such as iron or ferrite, wound with conductive coils. Consequently, they are sometimes referred to as wire-wound core devices.
One major difficulty with wire-wound core devices is that they have been difficult to miniaturize. While components such as resistors, diodes, capacitors and transistors have been shrunk to the microscopic level, wire-wound core devices remain bulky and typically must be assembled as complete units before being applied in hybrid circuits.